Apparatus and method for aiding formation of bone forming material

ABSTRACT

An apparatus and method for aiding formation of bone forming material in the region of a bone structure of a living being, especially a human being, has at least one pick-up coil having first and second terminals, each of which being d.c.-coupled to at least one electrode, each pair of electrodes connected to a respective at least one electrode. Each pair of electrodes straddles a region of the bone structure within which enhanced formation of bone structure, specifically callus, is desired. Field generating means is provided for inducing in the pick-up coil an a.c. current having gentle, gradual slopes, a frequency preferably below 100 c/s, and a magnitude which produces a current density of no more than 10 microamperes per square millimeter at the electrodes.

United States Patent [191 Kraus [4511 July 17,1973

APPARATUS AND METHOD FOR AIDING FORMATION OF BONE FORMING MATERIAL [76] Inventor: Werner Kraus, Bauerstrasse 31, D-8

Munich 13, Germany [22] Filed: Apr. 9, 1970 [21] Appl. No.: 26,809

[30] Foreign Application Priority Data Apr. 10, 1969 Germany P 19 18 299.1

[52] U.S. Cl l28/82.l, 3/1, 128/] R [51] Int. Cl. A6ln [58] Field of Search 128/82.1, 83, 87,

[56] References Cited UNITED STATES PATENTS 3,357,434 12/1967 Abel] 128/419 OTHER PUBLICATIONS Effects of Electric Currents on Bone in Vivo by Bassett et al., Nature, Nov. 14, 1964, Vol. 204, p. 652-654.

Induction Pacemaker for Control of Complete Heart Block by G. Holswade et al., Journal of Thoracic & Cardiovas, Surg. Vol. 44, No. 2, Aug. 1962, p. 246, 252.

Primary Examiner-Richard A. Gaudet Assistant Examiner-J. Yasko Att0meySpencer & Kaye [57] ABSTRACT An apparatus and method for aiding formation of bone forming material in the region of a bone structure of a living being, especially a human being, has at least one pick-up coil having first and second terminals, each of which being d.c.-coupled to at least one electrode, each pair of electrodes connected to a respective at least one electrode. Each pair of electrodes straddles a region of the bone structure within which enhanced formation of bone structure, specifically callus, is desired. Field generating means is provided for inducing in the pick-up coil an ac. current having gentle, gradual slopes, a frequency preferably below 100 c/s, and a magnitude which produces a current density of no more than 10 microamperes per square millimeter at the electrodes.

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APPARATUS AND METHOD FOR AIDING FORMATION OF BONE FORMING MATERIAL BACKGROUND OF THE INVENTION all, as in the case of pseudo-arthrosis or osteoporosis.

The apparatus and method described herein provide the possibility of accelerating the formation of bone forming material and correspondingly cutting down the period of time necessary for recovering from a fracture,

as well as the possibility to induce formation of bone where this ability has been impeded by a disorder such as osteoporosis.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a novel apparatus for helping bone disorders to mend, e.g. fractures or osteoporosis or other disorders of the mineral metabolism.

Another object of the present invention is to provide apparatus and methods to abbreviate the period of time which is necessary to bring a fractured limb into a state where it can be used again.

A further object of the invention is to provide an improved splint which promotes healing of the splinted fracture and is simultaneously of reduced size and weight, so that the wound trauma is reduced and the aftereffects of the fracture are alleviated.

Features of the present invention include an apparatus for aiding formation of bone forming material in a region of the bone structure of a living being which comprises at least one pick-up coil having first and second terminals. At least one first electrode of elongated, slender shape adapted to be inserted into the bone structure is connected to the first terminal. A second electrode is positioned at least partially on the side of the bone structure which is opposite to said first electrode, and is d.c.coupled to a portion of said living being adjacent to said bone structure. Means are provided for inducing in the pick-up coil or coils a current having gentle, gradual slopes; e.g. a current in the fonn of a sine wave having a low harmonics content which may be as low as percent, preferably lower than 10 percent or in the form of a triangular wave, a frequency below 1,000 c/s, preferably below 100 or 60 c/s, and a magnitude which produces a current density of no more than 10 microamperes per square millimeter, preferably between 3 and 7 microamperes per square millimeter, at the electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic elevation view, partially in cross section, of an apparatus according to the present invention applied to a fractured bone;

FIG. 2 is a schematic perspective view of an embodiment of a novel splint according to the present invention attached to a broken bone;

FIG. 3 is an enlarged cross-sectional view taken generally along the line III-III in FIG. 2;

FIG. 4 is a somewhat enlarged cross-sectional view taken generally along the line IV-lV in FIG. 2;

FIG. 5 is a schematic elevation view, partly in cross section, of a further embodiment of a novel splint structure;

FIG. 6 is a schematic view partly in cross section, of still another embodiment of a novel splint applied to a fractured bone to be mended;

FIG. 7 is a schematic perspective view of yet another embodiment of a new splint structure attached to a broken bone.

DESCRIPTION OF THE PREFERRED EMBODIMENTS There is shown in FIG. 1 a bone 10 of a living being, e.g. an femur (thigh bone) of a human being, which has gaps l2, 14 caused by a fracture.

The parts of the fractured bones are fixed in the normal position by means of two opposed splints l6, 18 which may be fixed to the parts of the broken bone by means of screws as usual in the medical art. The splints may be made of a stainless steel material or a Co-Cr alloy known as Vitallium" and may have the form of a curved plate.

To the main surface of splint 16., which is opposite to the bone 10, is attached a pick-up arrangement which includes a rod-like magnetic core 20 hearing three pick-up coils 22, 24, 26. The core and the coils are an capsulated in an appropriate plastic material 28. The core is made of a material having low reluctance, such as a magnetically soft ferrite or Permalloy. A first terminal of coil 22 is electrically connected, or d.c. coupled, to splint l6, and the second terminal of coil 22 is connected through an insulated wire 30 to two rod-like electrodes 32. The insulation of the wire 30 extends up to the point where the conductor enters the bone 10, or more specifically the gap 12 between the bone portions separated by the fracture.

The first (the upper in FIG. 1) terminal of coil 24 is connected to an insulated wire which passes into the bone 10 through a hollow screw v334 insulated against the splint 16. The wire extends preferably into the endostale bone or marrow cavity of the bone 10 and is bare beginning from the point where it leaves screw 34. The other (lower) terminal of coil 24 is connected to a screw 36 which is insulated against splint 16, but has a bare tip which extends into the bone 10, preferably as far as into the endostale bone or marrow cavity, and forms an electrode.

The lower terminal of coil 26 is again connected to splint l6, and the other terminal of coil 26 is connected through an insulated wire 38 both to a rod-like elec trode 40, which extends radially into gap 14, and to the second splint 18 which may be fixed to the portions of bone 10 by screws (not shown) in the usual manner.

A tube-like field coil 42 is provided which may be slipped over the broken limb into the position shown in FIG. 1. Field coil 42 comprises a plurality of windings encompassing the broken limb and, thus, magnetic core 20 bearing pickup coils 22, 24 and 26. The field coil 42 is connected to an a.c. signal generator 44 which may be of known construction and supplies to coil 42 an alternating current, e.g. a sinusoidal current having a low harmonics content which may be less than 20 percent, preferably less than 10 or 5 percent. The signal delivered by the a.c. signal generator has a frequency of less than 1,000 c/s, preferably less than I00 or 60 c/s, e.g. between 1 or 10 c/s and 40 c/s. The signal generator 44 may comprise a modulator for superimposing higher frequency oscillations onto the basic signal; these oscillations or undulations may have a frequency which is at least three times the frequency of the basic signal.

When excited by signal generator 44, field coil 42 produces an alternating magnetic field symbolized in FIG. 1 by field lines 48 which are picked up by core 20 and induce alternating currents in the coils 22, 24, 26, so that alternating currents or potentials are produced between the spaced electrodes connected to the terminals of said coils. It is these alternating currents or potentials having gradual, gentle slopes, low harmonics content and low frequency, which greatly enhance the formaton of bone forming material, or callus. Callus forming rates which are more than three to five times faster than the normal rates have been observed in human beings to which the present apparatus and method were applied for healing a fracture. Further callus formation could be induced in pathological cases where normal callus formation had failed, as in the case of pseudo-arthrosis.

The recovery of the broken bone is further aided by the magnetic field which is produced by field coil 42 and which is essentially parallel to the structural elements of the bone to be formed.

A further embodiment of a splint for use in the present apparatus and method is depicted in FIGS. 2, 3 and 4. Splint 50 has the form of an elongated, curved plate which is attached to a broken bone 52 by screws 54. The splint 50 has a circumferencial groove 56 (see FIG. 3) into which one or several pick-up coils 58 are wound. Groove 56 housing the pick-up coil or coils 58 is enclosed with an appropriate plastic material or resin 60, e.g. an epoxy resin. The coil ends extend into bores of the bone or the gaps in the bone caused by the fracture, as shown in FIG. 4. The portion of the wires between the coil proper and the point of entrance into the bone or gap is insulated, e.g. by a teflon insulation, the bare tip of the wire forming an electrode. One of the coil ends may be connected to a screw 54 which may or may not be insulated against the splint.

The pick-up coils cooperate with a field coil (see FIG. 2) which is positioned in the vicinity of splint 50 and functions in a manner similar to coil 42 shown in FIG. 1.

FIG. shows a splint 60 which is externally applied to an injured limb, i.e. to the skin 62 thereof. The splint 60 may be of any suitable material, e.g. a plastic or resin material which is hardened in situ, and comprises pointed spine-like members 64, the roots of which are embedded in the material forming the splint 60 proper. The pointed ends 66 of members 64 are inserted into the broken bone 68, preferably as far as the marrow channel as shown in FIG. 5, to fix the bone in its proper position. Simultaneously, the pointed ends 66 being of metal serve as electrodes and are connected to respective pick-up coils 70 which are similar to those described in connection with FIG. 2. The portions of members 64 which are outside of bone 68 are insulated against the tissue 72 surrounding the bone 68. In operation, a current is induced in coils 70, e.g. by a pick-up coil as shown in FIG. 2 or by the stray-fields which exist in the environment and are caused by the mains, electrical appliances,and so on.

FIG. 6 shows a splint according to the present invention which is in general similar to the splint shown in FIG. 5 and comprises a plastics or resin material 80,

shaped and cured in situ on the skin 82 of the outer side of an injured hand comprising broken bones 84. The main difference between the splints according to FIG. 5 and 6 respectively, is that a capacitor 88 is connected in parallel to pick-up coil 86 for tuning it to the frequency of the induced currents. The capacitor 88 is embedded in material and provides for an especially low harmonics content of the induced signal, which will produce a purely sinusoidal current.

As noted above, a major advantage of the present in. vention is that callus is formed so quickly that the broken bone will be able to recover to a substantial portion of its original strength in a relatively short time, so that the splint need not supplement the load carrying function of the bone when the injured individual has otherwise recovered sufficiently to be able to get up again. Thus, the splint is only needed for fixing the broken bone in the proper position during the initial stage of healing and can be made much lighter and thinner than the presently used splints. The screws used to attach the splint to the bone may be correspondingly smaller, which greatly reduces the wound trauma and the after effects which arise after removal of the splint; e.g. the filling of the screw holes with bone forming material. Further, the use of the so-called Kuentscher-nail a rod-like supporting element, inserted into the marrowchannel of a broken bone) may be dispensed with.

FIG. 7 shows a novel splint of such reduced dimensions, the splint comprises a curved plate-like member 90, made of stainless steel or Vitallium, to which pick-up coil means 92 wound around a magnetic core 94 are attached. Member may be made of sheet material having a thickness of l to 2 mm in contrast to 4 to 6 mm in the known splints. Member 90 is connected to one terminal of each of the coils making up coil means 92 through an unsymmetrically conducting device 99, such as a diode, to make the shape of the current wave unsymmetrical. Preferably, member 90 is positive during the current periods having the higher amplitude.

Pick-up coil means 92 is connected by insulated leads 96 to bare, slender, rod-like electrodes 98 adapted for insertion into a bone structure (e.g. as shown in FIG. 4) to aid forming or regeneration of bone material.

The electrode portions which are in contact with the bone structure consist preferably of a noble-metal alloy, e.g. an alloy of 90 percent by weight Pt and 10 percent by weight Ir, or stainless alloys such As a Co-Cralloy known as Vitallium." The insulation may consist of Teflon, and all of the materials which are in contact with bone or tissue are of course so chosen that they are compatible with the environment and the living or organic matter.

The induced current which enters into the bone region may consist, e.g., of a sinusoidal wave having low harmonics content, a triangular wave, a series of triangular or essentially sinusoidal pulses of alternating polarity; the said pulses being separated by periods of time during which the current is zero or negligible. The waveforms or pulses need not to be symmetrical.

The invention is not limited to healing fractured bones, it may be applied with success also for curing other bone disorders where forming of bone material is to be enhanced or promoted. Thus, the invention may be applied, e.g., to curing osteoporosis, regenerating bone structure destroyed by a tumor, to cure an illness known as Sudecksche Atrophia and so-called false articulations (pseudo-arthrosis The pick-up coil means may also be positioned adjacent the peripheral edge, e.g. at the straight long edge portion, of the plate member of the splint.

EXAMPLE I A novel splint similar to that shown in FIG. 2 was attached and electrodes which were in the form of needles consisting of a platinum-iridium alloy, were applied as shown in FIG. 4 to the broken right femur (upper thigh bone) of a rabbit. A similar splint and similar electrodes, however, without being connected to a pick-up coil or other current source were applied to the like-wise broken left femur of the same animal. This was carried out in an operation under narcosis lege artis. The animal was kept in a barn within which an electric a.c. field was maintained producing in the windings of the pick-up coil and a.c. current of sinusoidal waveshape and a frequency of 25 c/s. The maximum current density at the areas of contact between the electrodes and the tissue or bone was about 5 microamperes per square millimeter. After having been kept in the electric field for 3 weeks, the rabbit was killed and sections of the bones in the planes of the electrodes were pre pared. The sections showed that at least three times as much callus had formed in the area of those electrodes which were connected to the pick-up coil in comparison with the area connected to the other, currentless dummy electrodes.

EXAMPLE II Similar results as in example I have been achieved in mending an injured bone of a human being: A splint similar to that shown in FIG. 7 (without diode 99) was applied to the femur of a male (age about 50) which had been injured in a car accident about I year ago. The fracture did not heal because callus did not form by itself.

The applied novel splint comprised a metal plate of usual size to which a pick-up coil was attached having 200 windings of teflon-insulated platinum wire (diameter 0.] millimeters) wound on a magnetic core consisting of two superimposed Permalloy sheets each having a length of 50 mm, a width of 4 mm and a thickness of 0.5 mm. The electrodes connected to the terminals of the pick-up coil and inserted into the gap of the fractured bone were needle-like members consisting of an alloy of 90 percent by weight platinum and 10 percent by weight iridium and having a diameter of about 0.5 to 1 mm.

A field coil was putaround the splinted limb and excited by a sine-wave a.c. current of 25 c/s to produce an a.c. field of about 800 ampere-turns in the region of the pick-up coil.

After the splinted limb had been kept in the electric field and treated as described for l4 days, an x-ray investigation showed that plenty of new callus has formed in the area around and between the electrodes.

The patient who was regarded as incurable before the described treatment eventually completely recovered.

Other embodiments will occur to those skilled in the art and are within the following claims.

What is claimed is:

1. An apparatus for aiding formation of bone forming material in the region of a bone structure of a living being, comprising, in combination; at least one pick-up coil having first and second terminals, at least one first electrode of elongated slender shape electrically connected to said first terminal and adapted to be inserted into the bone structure; said second terminal being adapted to be conductively connected to the bone structure; a second electrode adapted to be positioned at least partially on the side of the bone structure which is opposite to said first electrode for being d.c.-coupled to a portion of the living being; and means for inducing in said pick-up coil, and between said electrodes, an a.c. current having gradual, gentle slopes, a frequency below 1,000c/s, and a magnitude which produces a current density of no more than 10 microamperes per square millimeter at said electrodes.

2. The apparatus according to claim 1 wherein said current inducing means comprises a field coil coupled to an a.c. signal generator.

3. The apparatus according to claim 1 wherein said current inducing means comprises the stray fields of the mains.

4. The apparatus according to claim 2 wherein said a.c.signal generator comprises means for superimposing on said a.c.signal a modulating signal having a frequency of at least three times the frequency of said a.c. signal.

5. The apparatus according to claim 1 for treating a, bone structure having an opening which is a gap caused by a fracture, wherein said second electrode is a metal splint adapted to be attached to the bone structure for fixing it.

6. The apparatus according to claim 5 wherein said metal splint comprises a plate-like member having a circumferential groove housing said pick-up coil.

7. The apparatus according to claim 5 wherein said pick-up coil is wound around a core of a material of low reluctance, said core forming an open-ended magnetic circuit.

8. The apparatus according to claim 1, further including a capacitor connected in parallel to said pickup coil to form a resonant circuit tuned substantially to the frequency of the induced current.

9. The apparatus according to claim 1, wherein the frequency is below c/s and preferably between 1 and 65 c/s.

10. The apparatus according to claim 1, wherein said frequency is between about 10 and 30 c/s.

11. The apparatus according to claim 1, wherein said harmonics content is below 20 percent and preferably below 10 percent. 7

12. The apparatus according to claim 1, wherein said current density at said electrodes is below 10 microamperes per square millimeter, and preferably between 3 and 7 microamperes per square millimeter.

13. The apparatus according to claim 1, wherein the coil and the coil leads are insulated up to the point where the electrodes are adapted to enter into the bone structure.

14. The apparatus according to claim 1 wherein said pick-up coil is mechanically connected to a medical splint adapted to reinforce and fix the bone structure.

15. The apparatus according to claim 1 wherein said frequency is between 10 c/s and 1,000 c/s.

16. In an apparatus for aiding formation of bone forming material in the region of a bone structure of a living being including a splint for positioning the bone, and means for securing the splint to the bone, the improvement comprising at leastone first electrode of elongated slender shape adapted to be inserted into the bone structure; a second electrode adapted to be positioned at least partially on the side of the bone structure which is opposite to said first electrode for being d.c.-coupled to a portion of the living being; and, at least one pick-up coil having a first terminal and a second terminal, said first terminal being connected to said first electrode and said second terminal being adapted to be conductively connected to the bone structure, said coil being adapted to be arranged in inductive relationship with a signal generating means for inducing within said coil an a.c. current having gradual, gentle slopes, a frequency below 1,000 c/s, and a magnitude which produces a current density of no more than 10 microamperes per square millimeter at said electrodes.

17. The apparatus as defined in claim 16, further comprising: a screw having at least its outer surface made of insulating material and connecting the splint to the bone structure and wherein said first electrode is located within said screw so that said first electrode is insulated from the splint.

18. The apparatus as defined in claim 16, wherein the splint is a plate-likemember made of a non-magnetic material and said second terminal is connected to the splint.

19. The apparatus as defined in claim 18, wherein said plate is a sheet-metal member having a thickness not greater than 3 millimeter.

20. The apparatus as defined in claim 16 further comprising a rod-shaped magnetic core and wherein said pick-up coil is wound on said magnetic core. 

1. An apparatus for aiding formation of bone forming material in the region of a bone structure of a living being, comprising, in combination; at least one pick-up coil having first and second terminals, at least one first electrode of elongated slender shape electrically connected to said first terminal and adapted to be inserted into the bone structure; said second terminal being adapted to be conductively connected to the bone structure; a second electrode adapted to be positioned at least partially on the side of the bone structure which is opposite to said first electrode for being d.c.-coupled to a portion of the living being; and means for inducing in said pick-up coil, and between said electrodes, an a.c. current having gradual, gentle slopes, a frequency below 1,000c/s, and a magnitude which produces a current density of no more than 10 microamperes per square millimeter at said electrodes.
 2. The apparatus according to claim 1 wherein said current inducing means comprises a field coil coupled to an a.c. signal generator.
 3. The apparatus according to claim 1 wherein said current inducing means comprises the stray fields of the mains.
 4. The apparatus according to claim 2 wherein said a.c.signal generator comprises means for superimposing on said a.c.signal a modulating signal having a frequency of at least three times the fRequency of said a.c. signal.
 5. The apparatus according to claim 1 for treating a, bone structure having an opening which is a gap caused by a fracture, wherein said second electrode is a metal splint adapted to be attached to the bone structure for fixing it.
 6. The apparatus according to claim 5 wherein said metal splint comprises a plate-like member having a circumferential groove housing said pick-up coil.
 7. The apparatus according to claim 5 wherein said pick-up coil is wound around a core of a material of low reluctance, said core forming an open-ended magnetic circuit.
 8. The apparatus according to claim 1, further including a capacitor connected in parallel to said pick-up coil to form a resonant circuit tuned substantially to the frequency of the induced current.
 9. The apparatus according to claim 1, wherein the frequency is below 150 c/s and preferably between 1 and 65 c/s.
 10. The apparatus according to claim 1, wherein said frequency is between about 10 and 30 c/s.
 11. The apparatus according to claim 1, wherein said harmonics content is below 20 percent and preferably below 10 percent.
 12. The apparatus according to claim 1, wherein said current density at said electrodes is below 10 microamperes per square millimeter, and preferably between 3 and 7 microamperes per square millimeter.
 13. The apparatus according to claim 1, wherein the coil and the coil leads are insulated up to the point where the electrodes are adapted to enter into the bone structure.
 14. The apparatus according to claim 1 wherein said pick-up coil is mechanically connected to a medical splint adapted to reinforce and fix the bone structure.
 15. The apparatus according to claim 1 wherein said frequency is between 10 c/s and 1,000 c/s.
 16. In an apparatus for aiding formation of bone forming material in the region of a bone structure of a living being including a splint for positioning the bone, and means for securing the splint to the bone, the improvement comprising at least one first electrode of elongated slender shape adapted to be inserted into the bone structure; a second electrode adapted to be positioned at least partially on the side of the bone structure which is opposite to said first electrode for being d.c.-coupled to a portion of the living being; and, at least one pick-up coil having a first terminal and a second terminal, said first terminal being connected to said first electrode and said second terminal being adapted to be conductively connected to the bone structure, said coil being adapted to be arranged in inductive relationship with a signal generating means for inducing within said coil an a.c. current having gradual, gentle slopes, a frequency below 1,000 c/s, and a magnitude which produces a current density of no more than 10 microamperes per square millimeter at said electrodes.
 17. The apparatus as defined in claim 16, further comprising: a screw having at least its outer surface made of insulating material and connecting the splint to the bone structure and wherein said first electrode is located within said screw so that said first electrode is insulated from the splint.
 18. The apparatus as defined in claim 16, wherein the splint is a plate-like member made of a non-magnetic material and said second terminal is connected to the splint.
 19. The apparatus as defined in claim 18, wherein said plate is a sheet-metal member having a thickness not greater than 3 millimeter.
 20. The apparatus as defined in claim 16 further comprising a rod-shaped magnetic core and wherein said pick-up coil is wound on said magnetic core. 